The present invention relates to a head positioning device having an actuator of two-stage structure, and a disk drive using the same.
With the evolution of multimedia in recent years, there are strong demands in the market for such disk drives having high recording density with a capability of positioning a head promptly into a target position on a recording medium of discoidal shape, to read and/or write a large volume of image data, sound data, text data and the like at high speed. There are also proposed a variety of techniques for positioning a head at high speed with high accuracy. As the techniques of achieving the high-speed and high-accuracy positioning, some of them draw attention as they employ a method of controlling two drive mechanisms, a main drive mechanism and a subsidiary drive mechanism, in such a manner as to function cooperatively to position the head.
The main drive mechanism is used primarily for a large motion of the head such as a seek operation and jumping across a plurality of tracks, and it rotates a head support mechanism by using a voice coil motor (hereinafter referred to as xe2x80x9cVCMxe2x80x9d) or the like around a shaft mounted to a chassis to move the head and head slider. The subsidiary drive mechanism is used mainly for a high-speed minute positioning of the head such that it follows a track, jumps over a single track and the like, and it is controlled over a wide band, but within a small movable range, by a piezo-electric component such as a piezo element, disposed to a tip end of the main drive mechanism to position the head and the head slider with a quick response. A drive mechanism provided with the main drive mechanism and the subsidiary drive mechanism is generally called two-stage actuator or piggyback actuator. The main drive mechanism and the subsidiary drive mechanism are called coarse actuator and fine actuator respectively. The control method using a two-stage actuator for positioning of the head as described above is proposed as one of the high-speed and high-accuracy positioning techniques (Japanese Patent Laid-open Publication, No. H10-255418, for example).
A piezo element used as the fine actuator, in particular, has functions of both a piezoelectric effect and a reverse-piezoelectric effect. That is, the piezo element has a capability of positioning control by using a minute displacement due to a strain produced as the reverse-piezoelectric effect by a control voltage, while it also capable of detecting a minute distance of displacement using a voltage generated with the piezoelectric effect by the displacement. Another technique of controlling an actuator called self-sensing actuator is thus proposed, using both of the above functions (refer to Transactions of the Japan Society of Mechanical Engineers, Vol. 64, No. 624, pages 2931-2937, published August 1998, under the title of xe2x80x9cTracking control of a cantilever beam using self-sensing actuator based on virtual bridge circuitxe2x80x9d). In addition, a control technique of the two-stage actuator is also proposed as the technique that applies the above actuator control technique to a disk drive, in which a piezo element defining the fine actuator is mounted to a head support mechanism driven by a coarse actuator, thereby making it capable of controlling high-speed and high-accuracy positioning by using both functions of the piezoelectric effect and the reverse-piezoelectric effect of the piezo element (Japanese Patent Laid-open Publication, No. S60-35383, for example).
Furthermore, there is also proposed another technique of controlling the two-stage actuator, in which a fine actuator using a piezo element is made to function as a sensor for detecting vibrations and/or impacts applied to a disk drive for the purpose of correcting a displacement of a head position due to the vibrations and/or the impacts (e. g., Japanese Patent Laid-open Publication, No. H04-330679).
FIG. 5 depicts a structural diagram of a head positioning device provided with a two-stage actuator and is capable of making correction of any displacement of a head position due to vibrations and the like by using its fine actuator to function as a vibration sensor. Referring now to FIG. 5, the head positioning device will be described hereafter as an example of the prior art.
In FIG. 5, magnetic head 12 (hereinafter referred to as xe2x80x9cheadxe2x80x9d), which reads and write data to and from magnetic disk 11 (hereinafter referred to as xe2x80x9cdiskxe2x80x9d), i.e. a kind of recording media of a discoidal shape, is mounted integrally to a tip of head slider 13. The head slider 13 is mounted to a tip end of fine actuator 52, and the fine actuator 52 is connected to one end of head support mechanism 14. The head support mechanism 14 is driven by coarse actuator 51 to rotate about rotary shaft 140 mounted to a main body of the disk drive, and to position the head 12 in cooperation with function of the fine actuator 52. Furthermore, the coarse actuator 51 moves the head support mechanism 14 including the head 12 to a target position xe2x80x9cRxe2x80x9d in response to coarse motion drive signal xe2x80x9cd1xe2x80x9d from control unit 96. The fine actuator 52 is controlled by fine motion drive signal xe2x80x9cd2xe2x80x9d of the control unit 96 in a manner that the head 12 mounted to the tip end of the head support mechanism 14 is displaced, or shifts, slightly by distance xe2x80x9cY2xe2x80x9d from center position xe2x80x9cY1xe2x80x9d located along a line extending from the head support mechanism 14. The head 12 reads present position signal xe2x80x9cyxe2x80x9d indicating position xe2x80x9cYxe2x80x9d, where the head 12 is located presently, from a servo data recorded beforehand on the disk 11. At the same time, the displacement distance xe2x80x9cY2xe2x80x9d of the fine actuator 52 from the center position xe2x80x9cY1xe2x80x9d to the head position xe2x80x9cYxe2x80x9d can be detected using a piezo element or the like. In this instance, the piezo element detects the actual distance xe2x80x9cY2xe2x80x9d of a minute displacement of the fine actuator 52 to produce relative displacement signal xe2x80x9cy2xe2x80x9d. The control unit 96 receives the present position signal xe2x80x9cyxe2x80x9d, the relative displacement signal xe2x80x9cy2xe2x80x9d and target position signal xe2x80x9crxe2x80x9d directed to it for a movement toward the target position xe2x80x9cRxe2x80x9d, performs respective computations, and produces coarse motion drive signal xe2x80x9cd1xe2x80x9d and fine motion drive signal xe2x80x9cd2xe2x80x9d. The head 12 is positioned into the target position xe2x80x9cRxe2x80x9d according to these drive signals obtained as a result the computations. The structure discussed above thus accomplishes positioning control to the target track.
In this example of the prior art, the control unit 96 additionally receives gate signal xe2x80x9cgxe2x80x9d for vibration detection. The control unit 96 detects external vibrations in response to a command given by the gate signal xe2x80x9cgxe2x80x9d for vibration detection, and corrects any deviation in position of the head due to the vibrations and the like.
FIG. 6 depicts an operational timing chart illustrating an operation for correcting an influence of external vibrations in the example of the prior art. As shown in FIG. 6, this head positioning device of the prior art uses coarse actuator 51 to carry out rough positioning from time 0 to time T1. It further carries out the positioning from time T1 to time T2 in a manner to locate the head 12 into a target track by displacing the fine actuator 52 to such an extent as shown by the displacement distance xe2x80x9cY2xe2x80x9d. It then holds the fine actuator 52 to maintain the displacement distance constant for duration between time T2 and time T3, or a gate period, and detects vibration data from the fine actuator 52 in response to the gate signal xe2x80x9cgxe2x80x9d for vibration detection. In other words, the control unit 96 keeps the displacement distance xe2x80x9cY2xe2x80x9d of the fine actuator 52 unchanged when the head 12 reaches the target position xe2x80x9cRxe2x80x9d. During this period, the fine actuator 52 itself functions as a sensor, and the control unit 96 uses relative displacement signal xe2x80x9cy2xe2x80x9d as the vibration data. In addition, the control unit 96 feeds back the vibration data into control signals of the fine actuator 52 and the coarse actuator 51 to drive them in a manner to cancel any deviation caused by the vibrations.
Accordingly, the above example of the prior art can also make correction of deviation in position of the head due to vibrations. Furthermore, it can be constructed at low cost since it uses the fine actuator 52, which is inherently provided for the purpose of head positioning, as means for detecting vibrations, without having any additional element such as an acceleration sensor specifically for the vibration detection.
However, the above example of the prior art has a problem that it can not perform correction against vibrations occurring during a seek operation, for instance, because it is unable to detect vibrations during any other time than the period directed by the gate signal xe2x80x9cgxe2x80x9d for vibration detection.
That is, the above example has the capability of detecting external impacts and vibrations and making correction of a deviation in position of the head during an operation following the moment when the head reaches near the target position, or the period between time T2 and time T3 as shown in FIG. 6. However, the fine actuator 52 cannot be used as a sensor for detecting the vibrations and impacts while the head 12 is in motion such as in the period from time 0 to time T2. Therefore, it tends to fail proper correction of a deviation of the head position, if it receives external impacts and/or vibrations during such period, and thereby it is likely to take a longer time to complete the positioning.
As described above, the prior art example is liable to increase the time it requires for the positioning, since the head 12 tends to shift substantially from the prescribed position if there are external impacts and/or vibrations while the head 12 is in motion.
The present invention is devised to solve the foregoing problems, and intended to provide a head positioning device capable of performing positioning control with stable operation at all times even when it receives external vibrations and impacts. This is achieved by adding a simple element to a positioning control system having a two-stage actuator. The invention also provides a disk drive using the same head positioning device.
To accomplish the above object, the head positioning device of this invention comprises an actuator, or head moving means provided with a coarse actuator and a fine actuator, and control means for controlling the actuators to function cooperatively to move and position the head to a target position in a manner that an absolute value of displacement distance of the fine actuator is reduced to a minimum. Furthermore, the control means has a structure that comprises positioning control means for generating a control signal to control positioning of the coarse actuator and the fine actuator, vibration detection means for extracting only a high frequency component contained in a signal corresponding to a magnitude of the displacement distance of the fine actuator, and disturbance correction means for combining the high frequency component with the control signal.
According to the above structure, the vibration detection means extracts only the high frequency component contained in the signal corresponding to the displacement distance of the fine actuator, as a vibrating component caused by the external disturbances. The disturbance correction means corrects an influence of the external disturbances using the extracted vibrating component. As a result, the head positioning device can use the inherently provided fine actuator to detect the external disturbances without needing any provision of additional acceleration sensor and the like. Besides, the vibration detection means separates and extracts the vibrating component produced by the external disturbances according to its frequency, from a regulating component required for the positioning control, as contained in the signal corresponding to the displacement distance of the fine actuator. The head positioning device of the present invention can therefore detect the vibrating component due to external disturbances without being restricted by time such as a time period during which the fine actuator is held at the prescribed distance of displacement. According to the present invention, the head positioning device can thus correct an adverse effect of the external disturbances to the positioning control at any time when it is operating, so as to reduce degradation of a positioning accuracy resulting from the disturbances during the operation.
Moreover, the head positioning device of the present invention comprises a fine actuator for making fine positioning of a head mounted to it for reading and/or writing data on a discoidal recording medium, a coarse actuator for making rough positioning of the head by moving a head support mechanism equipped with the fine actuator, and a control unit for controlling a displacement, or a shift, of the fine actuator as well as a movement of the head by the coarse actuator. Furthermore, the control unit comprises a fine motion controller, a coarse motion controller, a vibration detector, a fine motion corrector, and a coarse motion corrector. The fine motion controller receives a difference between a target position signal for positioning the head into a target position and a present position signal derived from a servo data on the recording medium read by the head, as an input of position error signal, and generates a fine motion control signal to control a magnitude of displacement of the fine actuator according to the position error signal. The coarse motion controller receives a relative displacement signal corresponding to the displacement distance of the fine actuator, and generates a coarse motion control signal to control a movement of the head by the coarse actuator based on this relative displacement signal. The vibration detector receives the relative displacement signal, extracts a high frequency component contained in the relative displacement signal, and uses the extracted high frequency component as a vibration detection signal to produce and output a fine motion correction signal and a coarse motion correction signal by amplifying the vibration detection signal with predetermined amplification factors. The fine motion corrector produces a signal by combining together the fine motion control signal and the fine motion correction signal, and outputs it as a fine motion composite signal. The coarse motion corrector produces another signal by combining together the coarse motion control signal and the coarse motion correction signal, and outputs it as a coarse motion composite signal. In this structure, the fine actuator is driven according to the fine motion composite signal, and the coarse actuator is driven according to the coarse motion composite signal.
According to this structure, a vibration detector extracts only a vibrating component attributable to the external disturbances as contained in the relative displacement signal from the fine actuator. A disturbance corrector performs correction of the influence resulting from the external disturbances by using the extracted vibrating component. As a result, it is not specially required to have an acceleration sensor or the like, but it can use the inherently provided fine actuator. In addition, the vibration detector separates and extracts the vibrating component produced by the external disturbances according to its frequency, from the regulating component for the positioning control, as contained in the relative displacement signal. Therefore, the head positioning device of the present invention can detect the vibrating component from the external disturbances without being restricted by time such as a time period during which the fine actuator is held at a prescribed distance of the displacement. According to the present invention, the head positioning device can thus correct an adverse effect of the external disturbances to the positioning control at any time when it is operating, so as to reduce degradation of a positioning accuracy resulting from the disturbances during the operation.
Furthermore, the head positioning device of the present invention has the fine actuator comprised of a piezo-electric element.
This structure enables the head positioning device to detect the relative displacement signal corresponding to the displacement distance of the fine actuator by using a piezoelectric effect of the piezo-electric element, and to control the displacement of the fine actuator at the same time by way of driving the fine actuator according to the fine motion composite signal using a reverse-piezoelectric effect.
Moreover, the head positioning device of the present invention has the vibration detector comprising a band-pass filter for extracting a signal component of high frequencies within a predetermined bandwidth, wherein the vibration detector outputs the signal component extracted by the band-pass filter as a vibration detection signal.
With this structure, the head positioning device can easily extract at all times the vibrating component resulting from the external disturbances contained in the relative displacement signal derived from the fine actuator. As a result, the head positioning device is not specially required to have an acceleration sensor or the like, but it can use the relative displacement signal from the inherently provided fine actuator to detect the vibrating component from the external disturbances without being restricted by time. In addition, the device can also use the detected vibration detection signal to reduce degradation of a positioning accuracy resulting from the disturbances during its operation.
Further, the head positioning device of the present invention has the vibration detector, which comprises a coring circuit having a nonlinear characteristic for removing a signal component of minute amplitude. The coring circuit has such a structure that receives a signal component of high frequency extracted by the band-pass filter, and outputs, as a vibration detection signal, a signal processed nonlinearly by use of the nonlinear characteristic.
This structure enables the head positioning device to separate the vibrating component produced by the external disturbances from the regulating component for positioning control, as contained in the relative displacement signal, and to detect the vibrating component more accurately. As a result, the device can effectively reduce degradation of the positioning accuracy resulting from the disturbances during its operation by using the detected vibration detection signal.
A disk drive of the present invention has a structure comprising the head positioning device described above.
The disk drive of this structure is not specially required to have an acceleration sensor or the like, but it can use the inherently provided fine actuator to detect external disturbances. In addition, the disk drive of this invention can detect the vibrating component due to the external disturbances without being restricted by time. According to the present invention, the disk drive can therefore correct an adverse effect of the external disturbances to the positioning control at any time when it is operating, so as to reduce degradation of a positioning accuracy resulting from the disturbances during the operation.